Earthquake source parameter estimation using synthetic waveform modelling

Fault plane solutions and focal depths for three crustal events occurring in the Himalayan collision zone have been obtained using synthetic waveform modelling. Two crustal events with their epicenters in the Tibetan plateau show large component of normal faulting with east-west trading T-axes. The third event with It’s epicenter north of Main Boundary Thrust (MBT) shows reverse faulting with the nodal planes paralleling the local structural trend. All the three crustal events studied have occurred at shallow focal depths of less than 15 km. The Inferred source parameters of these events are discussed In the light of active tectonics of the region.

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A seismological study of two Attica, New York earthquakes

Bulletin of the Seismological Society of America ◽

10.1785/bssa0680030641 ◽

1978 ◽

Vol 68 (3) ◽

pp. 641-651 ◽

Cited By ~ 1

Author(s):

Robert B. Herrmann

Keyword(s):

New York ◽

Source Parameters ◽

Focal Depth ◽

Strike Slip ◽

Focal Mechanisms ◽

The Other ◽

Nodal Plane ◽

Reverse Faulting ◽

Epicentral Intensity ◽

East West

abstract The Attica, New York earthquakes of January 1, 1966 and June 12, 1967 are studied in detail to obtain their focal mechanisms, depths and seismic moments. Both events have similar source parameters with one nodal plane striking about 120° and dipping 60°S and the other nodal plane striking about 20° and dipping 70°E. The fault motion on the NNE nodal plane has a component of right lateral strike slip and one of reverse faulting. Though this nodal plane parallels the Clarendon-Linden structure, the possibility of associating the other nodal plane with a diffuse east-west seismicity trend cannot be excluded. The shallow focal depth of 2 to 3 km for these two events can be used as an explanation of the relatively high epicentral intensity VIII of the Attica event of 1929.

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Fault Plane Solutions and the State of Stress in New England

Seismological Research Letters ◽

10.1785/gssrl.51.2.3 ◽

1980 ◽

Vol 51 (2) ◽

pp. 3-12

Author(s):

Timothy Graham ◽

Edward F. Chiburis

Keyword(s):

Stress Field ◽

New England ◽

Fault Plane ◽

The State ◽

Fault Plane Solutions ◽

Compressional Stress ◽

Southern New England ◽

State Of Stress ◽

Reverse Faulting ◽

East West

Abstract An analysis of eighteen New England fault plane solutions indicates that the area can be largely characterized by reverse faulting on north to northeasterly striking fault planes. This implies that New England is predominantly influenced by an east-west to southeast-northwest compressional stress field. This generalization may not apply in certain areas of southern New England.

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Fault plane solutions of earthquakes and active tectonics of the Tibetan Plateau and its margins

Geophysical Journal International ◽

10.1111/j.1365-246x.1989.tb02020.x ◽

1989 ◽

Vol 99 (1) ◽

pp. 123-154 ◽

Cited By ~ 385

Author(s):

Peter Molnar ◽

Hélène Lyon-Caent

Keyword(s):

Tibetan Plateau ◽

Fault Plane ◽

Active Tectonics ◽

The Tibetan Plateau ◽

Fault Plane Solutions

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A holistic seismotectonic model of Delhi region

Scientific Reports ◽

10.1038/s41598-021-93291-9 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Brijesh K. Bansal ◽

Kapil Mohan ◽

Mithila Verma ◽

Anup K. Sutar

Keyword(s):

Strain Energy ◽

Fault Plane ◽

Near Field ◽

Energy Estimates ◽

The West ◽

Fault Plane Solutions ◽

Northern India ◽

Structural Environment ◽

Reverse Faulting ◽

Using Data

AbstractDelhi region in northern India experiences frequent shaking due to both far-field and near-field earthquakes from the Himalayan and local sources, respectively. The recent M3.5 and M3.4 earthquakes of 12th April 2020 and 10th May 2020 respectively in northeast Delhi and M4.4 earthquake of 29th May 2020 near Rohtak (~ 50 km west of Delhi), followed by more than a dozen aftershocks, created panic in this densely populated habitat. The past seismic history and the current activity emphasize the need to revisit the subsurface structural setting and its association with the seismicity of the region. Fault plane solutions are determined using data collected from a dense network in Delhi region. The strain energy released in the last two decades is also estimated to understand the subsurface structural environment. Based on fault plane solutions, together with information obtained from strain energy estimates and the available geophysical and geological studies, it is inferred that the Delhi region is sitting on two contrasting structural environments: reverse faulting in the west and normal faulting in the east, separated by the NE-SW trending Delhi Hardwar Ridge/Mahendragarh-Dehradun Fault (DHR-MDF). The WNW-ESE trending Delhi Sargoda Ridge (DSR), which intersects DHR-MDF in the west, is inferred as a thrust fault. The transfer of stress from the interaction zone of DHR-MDF and DSR to nearby smaller faults could further contribute to the scattered shallow seismicity in Delhi region.

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The 25 October, 2018 Zakynthos (Greece) earthquake: seismic activity at the transition between a transform fault and a subduction zone.

Geophysical Journal International ◽

10.1093/gji/ggaa575 ◽

2020 ◽

Author(s):

P Papadimitriou ◽

V Kapetanidis ◽

A Karakonstantis ◽

I Spingos ◽

K Pavlou ◽

...

Keyword(s):

Spatial Clustering ◽

Accretionary Prism ◽

Velocity Model ◽

Strike Slip ◽

Double Difference ◽

Strain Partitioning ◽

Transform Fault ◽

Fault Plane Solutions ◽

The North ◽

Waveform Modelling

Summary The properties of the Mw = 6.7 earthquake that took place on 25 October 2018, 22:54:51 UTC, ∼50 km SW of the Zakynthos Island, Greece, are thoroughly examined. The main rupture occurred on a dextral strike-slip, low-angle, east-dipping fault at a depth of 12 km, as determined by teleseismic waveform modelling. Over 4000 aftershocks were manually analysed for a period of 158 days. The events were initially located with an optimal 1D velocity model and then relocated with the double-difference method to reveal details of their spatial distribution. The latter spreads in an area spanning 80 km NNW-SSE and ∼55 km WSW-ENE. Certain parts of the aftershock zone present strong spatial clustering, mainly to the north, close to Zakynthos Island, and at the southernmost edge of the sequence. Focal mechanisms were determined for 61 significant aftershocks using regional waveform modelling. The results revealed characteristics similar to the mainshock, with few aftershocks exhibiting strike-slip faulting at steeper dip angles, possibly related to splay faults on the accretionary prism. The slip vectors that correspond to the east-dipping planes are compatible with the long-term plate convergence and with the direction of coseismic displacement on the Zakynthos Island. Fault-plane solutions in the broader study area were inverted for the determination of the regional stress-field. The results revealed a nearly horizontal, SW-NE to E-W-trending S1 and a more variable S3 axis, favouring transpressional tectonics. Spatial clusters at the northern and southern ends of the aftershock zone coincide with the SW extension of sub-vertical along-dip faults of the segmented subducting slab. The mainshock occurred in an area where strike-slip tectonics, related to the Cephalonia Transform Fault and the NW Peloponnese region, gradually converts into reverse faulting at the western edge of the Hellenic subduction. Plausible scenarios for the 2018 Zakynthos earthquake sequence include a rupture on the subduction interface, provided the slab is tilted eastwards in that area, or the reactivation of an older east-dipping thrust as a low-angle strike-slip fault that contributes to strain partitioning.

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